The invention generally relates to a shock absorbing wheel suspension apparatus and a method of manufacturing same. More particularly, the invention is directed to a device used in bicycle single pivot suspension systems that is lightweight, reduces the number of components required for the system, and provides good performance and resistance to torsion, torque, and other forces on the suspension system.
Several types of bicycles, especially in the field of mountain bikes, include a variety of rear wheel suspension systems to attempt to improve performance and safety of bicycles and to increase comfort for bicycle riders. However, these suspension systems typically are very complicated structures involving many pivot points and/or several related components which result in increased and undesirable bulk and weight to the bicycle.
Although relatively more simple suspension systems providing only a single pivot point on the bicycle frame typically have fewer components, they still are commonly fabricated from a number of separate components, increasing inventory, design, and manufacturing costs, among other things. Moreover, those relatively simpler designs typically still are lacking with respect to their performance.
For example, one such suspension system is disclosed by U.S. Pat. No. 5,217,241 (to Girvin). The ""241 patent is directed to a bicycle with a wheel suspension having a single pivot axis requiring a rigid bridge tube connected to a seat tube and a down tube. The bridge tube positions the pivot point above the largest chain sprocket. Although this positioning of the pivot point is intended to translate pedal induced forces into forward motive forces, it actually provides a lifting moment to the suspension which is slight in the large chainring and greater in the smaller chainrings.
Although single-pivot designs such as the ""241 patent can be somewhat simple in construction and somewhat non-pedal-torque reactive in a certain chainring-gear combinations, they usually are very pedal-torque reactive in the chainring farthest away horizontally from the pivot. In the small chainrings, this construction typically lifts the bike and rider with an energy-wasting xe2x80x9cinchwormxe2x80x9d bobbing effect with each pedal stroke and its accompanying chain torque. This suspension does not adequately respond to bump loads under hard pedaling, as bump force must overcome the lifting moment in order to move the wheels in reaction to a bump. Also, due to its arc-like wheel path during shock absorption motion, the wheelbase dimension changes throughout the wheel""s stroke, causing kickback while pedaling.
In addition, the chain stays of the bike in the ""241 patent are vertically bent to clear the front derailleur and require a connecting tube between each of the chain stays to facilitate bracing the suspension system against transverse or lateral forces on the rear wheel. Moreover, the seat stays are attached to a shock absorbing element positioned behind the seat tube. Because this system relies primarily on the bridge tube and the connecting tube to resist transverse or lateral forces on the rear wheel, it requires also using a bulky and sometimes heavy swingarm, as well as overbuilding the pivot and pivot supports, to maintain sufficient or desirable rigidity, which adds undesirable weight to the bicycle.
Similarly, U.S. Pat. No. 5,284,354 (to McWethy) discloses a bicycle with a single pivot point rear wheel suspension system. The bicycle also discloses a cross bar or bridge tube to pivotably attach a rear wheel swing arm. The swing arm is vertically bent to clear the chain sprockets, and is laterally bent to accommodate a rear wheel axle. In addition, the bicycle has a bent seat tube, apparently in an attempt to improve performance of the shock absorber. However, this bike likewise suffers from the reliance of transverse support from the seat tube, the cross bar, and a gusset positioned between the two stays of the swing arm.
Other bikes have attempted to improve on these shortcomings, such as by securing both chain stays and seat stays to a linkage assembly positioned in front of a seat tube with a shock absorber attached to the linkage and to the bicycle frame. Examples of these bikes can currently be seen at the Internet websites for the bicycle companies, Santa Cruz Bicycles and Cannondale Bicycles.
The Santa Cruz website, for example, appears to disclose a complicated assembly to attach the seat stays and chain stays of a rear wheel swing arm to a bicycle frame. That connection assembly consists of two approximately vertically oriented support structures connected at their upper end to the forward ends of the seat stays, and connected at their lower end to a pivot point on the down tube of the bicycle frame. At an intermediate location, chain stays are welded to the outer sides of the support structures. In addition, and at approximately the same vertical location on the support structures, a brace is provided between those vertical structures. This brace apparently is intended to improve torque resistance of the linkage assembly. The complex construction of these assemblies, including the numerous separate elements of the assembly and the corresponding necessity for increased welding sites, results in a relatively heavy device with potential weak points occurring at the welding sites, as well as increases the amount of time and effort in construction of the assembly.
It is, therefore, an object of the invention to provide a single pivot suspension system useful, for example, in connection with the rear wheel of a bicycle such as a mountain bike, which addresses the shortcomings mentioned above.
Among other things, it is an object of the invention to provide a device to pivotably attach a rear wheel swing arm to a bicycle frame wherein the device includes a single elongated body; a connector attached to the body to pivotably connect the device to a bicycle frame; and at least one swing arm attachment element with at least one extension element to attach the forward portions of a rear wheel swing arm to the device. The device is sufficiently lightweight and strong to resist torsional forces occurring on the wheel suspension system. The device is also configured to attach to a shock absorber that is attached at its other end to the frame of the bicycle.
It is a further object of the invention to provide the device of the aforementioned character wherein the body of the device is generally tube-shaped, and in which the body and the attachment element are formed from a single piece of material.
It is yet another object of the invention to provide the device of the aforementioned character in which the extending portions each include confronting surfaces oriented toward the rear of the bicycle and angled with respect to a plane defined by a top tube, a down tube, and a seat tube of the bicycle frame.
It is still another object of the invention to provide a wheel suspension system having a single pivot axis about a frame in which the suspension system includes a seat stay and a chain stay attached at their rearward ends to a joint that attaches to an axle of a wheel; and attached at their forward ends to a linkage machined from a single piece of material, wherein the linkage has at least one extension element extending from the linkage to attach the seat stay and the chain stay, and in which the suspension system further includes an attachment piece to attach the wheel suspension system to the frame and to permit the wheel suspension system to pivot about the site of attachment. The suspension system is operably connected to a shock absorbing element positioned between the system and the frame.
It is yet another object of the invention to provide the system of the aforementioned character in which the seat stay and said chain stay are provided as a single element.
It is also an object of the invention to provide a forward attachment member for a single pivot bicycle rear wheel support, including at least one brace to attach a rearwardly positioned swing arm assembly; and a yoke to secure the attachment member at a pivot point on a frame of the bicycle, wherein the member and yoke are configured so that the pivot point is generally located on an average chain line in the bicycle""s normally laden position. The attachment member is also secured to one end of a shock absorber. The attachment member is configured to resist lateral forces that may occur on the rear wheel.
Another object of the invention is to provide an apparatus for suspending a wheel from a bicycle, including generally linear stay elements on each side of the wheel; a pivotable, generally tubular element extending in a generally upright direction having protruding portions formed integrally with the element to attach to the forward ends of the stay elements and configured to position the stays to permit free rotation of the bicycle wheel.
It is still another object of the invention to provide a rear wheel suspension for a bicycle having an elongated member formed from a single piece of material, in which the elongated element has at least one first connection element for operative attachment to a shock absorbing member, at least one second connection element for connection to a shock stay member, and at least one third connection element for connection to a chain stay member.
It is another object of the invention to provide a bicycle wheel suspension element that has a hollow body, a first attachment structure associated with the body for attaching said element to a pivot location on a bicycle frame, and a second attachment structure, with at least one lateral projection, spaced from the first attachment structure for attachment to at least one rearwardly projecting stay.
It is a still further object of the invention to provide a link to operably attach a rear wheel suspension apparatus to a pivotable connector on a bicycle, wherein the link includes a single generally tubular elongated body and at least one attachment element, both formed from a single piece of material. The attachment element preferably extends laterally from a longitudinal midline, to attach the rear wheel suspension apparatus.
It is another object of the invention to provide a method of manufacturing a single monolithic element as the central attachment element of a rear wheel suspension, including the steps of: a) forming the material for the element into an elongated piece having a cross-section with a central portion and at least one attachment portion protruding therefrom; b) shaping the outer surface of said element to remove some of the attachment portion along the length of the element, so that the attachment portion remains at at least one selected location along the length of the element; and c) removing unnecessary material from the inside of said element.
Other objects and advantages of my invention will be apparent from the following specification and the accompanying drawings, which are for the purpose of illustration only.